cp-decl.c (flag_conserve_space): New language specific flag to tell the compiler to use .common when possible.

	* cp-decl.c (flag_conserve_space): New language specific flag to
	tell the compiler to use .common when possible.  Reduces the size of
	.o files.
	* cp-decl.c (duplicate_decls): Copy DECL_COMMON from the olddecl.
	* cp-decl.c (start_decl): Set DECL_COMMON appropriately.
	* cp-decl.c (finish_decl): Use flag_conserve_space, instead of
	flag_no_common.
	* cp-decl2.c (flag_conserve_space, lang_f_options): New flag.
	* toplev.c (lang_options): New -fconserve-space flag.
	* tree.h (DECL_COMMON): New flag.
	* tree.h (tree_decl): New common_flag.
	* varasm.c (assemble_variable): Use DECL_COMMON to help determine if
	an object can be put in .common.
	* c-decl.c (start_decl): Set DECL_COMMON to 1..

From-SVN: r6244